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Tutur33
141 lines
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141 lines
11 KiB
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<h1 id="topic_header_text">L'instruction for</h1>
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<a href="Lesbouclesinstructionsforwhile.html">Les boucles (instructions for, while)</a> ››
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<p></p>
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<h4 class="rvps13"><span class="rvts0"><span class="rvts64">Syntaxe</span></span></h4>
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<p class="rvps8"><span class="rvts47">for</span><span class="rvts39"> élément </span><span class="rvts47">in</span><span class="rvts39"> séquence :</span><br/><span class="rvts81"> </span><span class="rvts39">bloc d'instructions</span><br/><span class="rvts40"># suite du programme</span></p>
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<p class="rvps7"><span class="rvts50">Les éléments de la séquence sont issus d'une chaîne de caractères ou bien d'une liste.</span></p>
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<h4 class="rvps13"><span class="rvts0"><span class="rvts64">Exemple avec une séquence de caractères</span></span></h4>
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<p class="rvps8"><span class="rvts40"># script Boucle4.py</span><br/><span class="rvts39">chaine = </span><span class="rvts53">'Bonsoir'</span><br/><span class="rvts47">for</span><span class="rvts39"> lettre </span><span class="rvts47">in</span><span class="rvts39"> chaine: </span><span class="rvts40"># lettre est la variable d'itération</span><br/><span class="rvts39"> </span><span class="rvts41">print</span><span class="rvts39">(lettre)</span><br/><span class="rvts41">print</span><span class="rvts53">("Fin de la boucle")</span></p>
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<p class="rvps8"><span class="rvts53">Exécuter </span><img alt="" style="padding : 1px;" src="lib/NouvelElement7.png"><span class="rvts11"> </span></p>
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<p class="rvps7"><span class="rvts11">La variable </span><span class="rvts17">lettre</span><span class="rvts11"> est initialisée avec le premier élément de la séquence (</span><span class="rvts72">'</span><span class="rvts17">B</span><span class="rvts72">'</span><span class="rvts11">).</span><br/><span class="rvts11">Le bloc d'instructions est alors exécuté.</span><br/><span class="rvts11">Puis la variable </span><span class="rvts17">lettre</span><span class="rvts11"> est mise à jour avec le second élément de la séquence (</span><span class="rvts72">'</span><span class="rvts17">o</span><span class="rvts72">'</span><span class="rvts11">) et le bloc d'instructions à nouveau exécuté...</span><br/><span class="rvts11">Le bloc d'instructions est exécuté une dernière fois lorsqu'on arrive au dernier élément de la séquence (</span><span class="rvts72">'</span><span class="rvts17">r</span><span class="rvts72">'</span><span class="rvts11">) :</span></p>
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<h4 class="rvps13"><span class="rvts0"><span class="rvts64">Exemple avec les éléments d'une liste</span></span></h4>
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<p class="rvps8"><span class="rvts40"># script Boucle5.py</span><br/><span class="rvts39">maliste = [</span><span class="rvts53">'Pierre'</span><span class="rvts39">, 67.5, 18]</span><br/><span class="rvts47">for</span><span class="rvts39"> element </span><span class="rvts47">in</span><span class="rvts39"> maliste:</span><br/><span class="rvts39"> </span><span class="rvts41">print</span><span class="rvts39">(element)</span><br/><span class="rvts41">print</span><span class="rvts53">("Fin de la boucle")</span></p>
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<p class="rvps8"><span class="rvts53">Exécuter </span><img alt="" style="padding : 1px;" src="lib/NouvelElement7.png"><span class="rvts11"> et tester</span></p>
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<p class="rvps7"><span class="rvts11">Là, on affiche dans l'ordre les éléments de la liste :</span></p>
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<h4 class="rvps13"><span class="rvts0"><span class="rvts64">Fonction </span></span><span class="rvts0"><span class="rvts94">range()</span></span></h4>
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<p class="rvps7"><span class="rvts11">L'association avec la fonction </span><span class="rvts17">range()</span><span class="rvts11"> est très utile pour créer des séquences automatiques de nombres entiers :</span></p>
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<p class="rvps8"><span class="rvts40"># script Boucle6.py</span><br/><span class="rvts41">print</span><span class="rvts39">(</span><span class="rvts41">list</span><span class="rvts39">(</span><span class="rvts41">range</span><span class="rvts39">(1,5)))</span><br/><span class="rvts47">for</span><span class="rvts39"> i </span><span class="rvts47">in</span><span class="rvts39"> </span><span class="rvts41">range</span><span class="rvts39">(1,5):</span><br/><span class="rvts39"> </span><span class="rvts41">print</span><span class="rvts39">(i)</span><br/><span class="rvts41">print</span><span class="rvts53">("Fin de la boucle")</span></p>
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<p class="rvps8"><span class="rvts38">>>></span><br/><span class="rvts42">[1, 2, 3, 4]</span><br/><span class="rvts42">1</span><br/><span class="rvts42">2</span><br/><span class="rvts42">3</span><br/><span class="rvts42">4</span><br/><span class="rvts42">Fin de la boucle</span></p>
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<h4 class="rvps13"><span class="rvts0"><span class="rvts64">Table de multiplication</span></span></h4>
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<p class="rvps7"><span class="rvts11">La création d'une table de multiplication paraît plus simple avec une boucle </span><span class="rvts17">for</span><span class="rvts11"> qu'avec une boucle </span><span class="rvts17">while</span><span class="rvts11"> :</span></p>
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<p class="rvps8"><span class="rvts40"># script Boucle7.py</span><br/><span class="rvts47">for</span><span class="rvts39"> compteur </span><span class="rvts47">in</span><span class="rvts39"> </span><span class="rvts41">range</span><span class="rvts39">(1,11):</span><br/><span class="rvts39"> </span><span class="rvts41">print</span><span class="rvts39">(compteur, </span><span class="rvts53">'* 9 ='</span><span class="rvts39">, compteur*9)</span><br/><span class="rvts41">print</span><span class="rvts53">("Et voilà !")</span></p>
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<p class="rvps8"><span class="rvts53">Exécuter </span><img alt="" style="padding : 1px;" src="lib/NouvelElement7.png"><span class="rvts11"> </span></p>
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<h3 class="rvps12"><span class="rvts0"><span class="rvts80">L'instruction </span></span><span class="rvts0"><span class="rvts95">break</span></span></h3>
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<p class="rvps7"><span class="rvts11">L'instruction </span><span class="rvts17">break</span><span class="rvts11"> provoque une sortie immédiate d'une boucle </span><span class="rvts17">while</span><span class="rvts11"> ou d'une boucle </span><span class="rvts17">for</span><span class="rvts11">.</span></p>
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<p class="rvps7"><span class="rvts11">Dans l'exemple suivant, l'expression </span><span class="rvts17">True</span><span class="rvts11"> est toujours ... vraie : on a une boucle sans fin.</span><br/><span class="rvts11">L'instruction </span><span class="rvts17">break</span><span class="rvts11"> est donc le seul moyen de sortir de la boucle.</span></p>
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<h4 class="rvps13"><span class="rvts0"><span class="rvts64">Affichage de l'heure courante</span></span></h4>
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<p class="rvps8"><span class="rvts40"># script Boucle8.py</span><br/><span class="rvts47">import</span><span class="rvts39"> time </span><span class="rvts40"># importation du module time</span><br/><span class="rvts47">while</span><span class="rvts39"> </span><span class="rvts41">True</span><span class="rvts39">:</span><br/><span class="rvts39"> </span><span class="rvts40"># strftime() est une fonction du module time</span><br/><span class="rvts39"> </span><span class="rvts41">print</span><span class="rvts39">(</span><span class="rvts53">'Heure courante '</span><span class="rvts39">, time.strftime(</span><span class="rvts53">'%H:%M:%S'</span><span class="rvts39">))</span><br/><span class="rvts39"> quitter = input(</span><span class="rvts53">'Voulez-vous quitter le programme (o/n) ? '</span><span class="rvts39">)</span><br/><span class="rvts39"> </span><span class="rvts47">if</span><span class="rvts39"> quitter == </span><span class="rvts53">'o'</span><span class="rvts39">:</span><br/><span class="rvts39"> </span><span class="rvts47">break</span><br/><span class="rvts41">print</span><span class="rvts53">("A bientôt")</span></p>
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<p class="rvps8"><span class="rvts53">Exécuter </span><img alt="" style="padding : 1px;" src="lib/NouvelElement7.png"><span class="rvts11"> et tester</span></p>
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<h3 class="rvps12"><span class="rvts0"><span class="rvts80">Astuce</span></span></h3>
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<p class="rvps7"><span class="rvts11">Si vous connaissez le nombre de boucles à effectuer, utiliser une boucle </span><span class="rvts17">for</span><span class="rvts11">.</span><br/><span class="rvts11">Autrement, utiliser une boucle </span><span class="rvts17">while </span><span class="rvts11">(notamment pour faire des boucles sans fin).</span></p>
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<p class="rvps4" style="clear: both;"><span class="rvts15">Créé avec HelpNDoc Personal Edition: </span><a class="rvts16" href="https://www.helpndoc.com/fr">Générateur de documentation complet</a></p>
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